The present technology relates to an information recording medium and a disc. Specifically, the present technology relates to the information recording medium which has a plurality of wobbled tracks and the disc for manufacturing the same.
There are many optical discs which adopt a wobble method in a CLV (Constant Linear Velocity) type optical disc format such as a write-once type and a rewritable type (R/RE) of a BD (Blu-ray Disc (registered trademark)), or a portion of a recordable DVD (Digital Versatile Disc), in order to create block and address. A wobble phase difference between adjacent tracks continuously changes in the optical disc of a CLV format compliance of the related art. If the wobble phase difference between the adjacent tracks meets certain conditions, it is possible to know a cause of deterioration of recording and reproduction characteristics or address reproduction characteristics.
FIG. 12 is a view showing the wobble phase difference between the adjacent tracks in BD. Since a main disc is made with very high accuracy, as substantially calculated from a BD standard, the wobble phase difference between the adjacent tracks changes from −180° to +180°, in approximately two rotation cycles.
In a case where the wobble phase of the adjacent track has a different phase, a groove center-to-center distance between the adjacent tracks periodically changes, and an unnecessary signal which has the same cycle as the wobble signal appears to a push-pull signal by optical interference. This is referred to as a wobble beat and becomes a cause of deteriorating an address reproduction performance. In addition, on the condition that the phases of an inner circumference track and an outer circumference track are close to the opposite phases, the unnecessary signal of the wobble signal cycle is also leaked to an RF (Radio Frequency) signal and becomes a cause of deteriorating a jitter of the RF signal. As for the recording, local heat transfer at the time of recording is changed by changing intervals (land width) between the adjacent tracks and becomes a cause which local deviation occurs in optimum recording conditions.
FIGS. 13A to 13D are schematic views showing four patterns which are extracted from periodical adjacent wobble phase changes. A groove format in which the recording and the reproduction of an information signal is performed on the groove is adopted in the BD. The wobble phases of three groove tracks Tn−1, Tn, and Tn+1, are shown in FIGS. 13A to 13D. Moreover, the wobble phases of FIGS. 13A to 13D respectively correspond to the positions shown in reference signs (A) to (D) in FIG. 12. Spots of laser beams are condensed on the track Tn in the center, and the track Tn is traced. In cases of FIG. 13A and FIG. 13C, either a track of the inner circumference or a track of the outer circumference and the wobble phase match with each other, but the wobble phase is inverted against the other track. In this state where phase relations of both sides are inverted against each other, an unnecessary signal component is leaked into the reproduction RF signal and becomes the worst-case conditions as reproduction characteristics. Also as for recording, a land width change between the adjacent tracks is largest and becomes a bad condition. In cases of FIGS. 13B and 13D, the phase between the adjacent tracks is shifted by the size of 90 degrees and the phases of the tracks on both sides are aligned. Under these conditions, a wobble beat component leakage into the reproduction RF signal is at a minimum and is best as an RF reproduction characteristic. Also a land width variation related to the recording is small as compared with the cases of FIGS. 13A and 13C.
FIG. 14 is a view schematically showing a relation between the wobble phase of the adjacent track and an RF jitter of an RUB (Recording Unit Block) unit. In a case where either wobble of the inner circumference or wobble of the outer circumference has the same phase and another wobble phase, it is possible to know that the deterioration of the RF jitter is most remarkable.
As shown in FIG. 15, it is desirable that the wobbles of the tracks adjacent to both sides of the inner circumferential side and the outer circumferential side have the same phases. Hereinafter, the wobble of the adjacent track is appropriately referred to as the “adjacent wobble.” In a state of the same phase, the wobble beat component does not occur. In addition, even if a wobble amplitude is increased in order to further improve the address reproduction performance, the recording and the reproduction characteristics are not affected. However, as shown in FIG. 15, it is not possible to match both adjacent wobbles of the inner circumferential side and the outer circumferential side with the phase in the existing CLV format compliance optical disc. For this reason, the phases between the adjacent wobbles are not matched, and the characteristics of an optical disc are decreased.
An optical disc in which a zone is divided in a radius direction and a frequency and the phase relation of the adjacent wobble are the same in one zone is suggested in order to stabilize a clock signal used for recording and reproduction of data in Japanese Unexamined Patent Application Publication No. 2003-123265.